Which statement about heat rate and efficiency relationship is correct?

• A. Higher heat rate means higher efficiency.
• B. Heat rate is total energy input per hour.
• C. Lower heat rate corresponds to higher efficiency.
• D. Heat rate and efficiency are unrelated.

Answer: (C)

The main idea here is that heat rate and efficiency move in opposite directions. Heat rate measures how much fuel energy is needed to produce one kilowatt-hour of electricity. If the heat rate is lower, you need less fuel energy to make each kWh, so a larger share of the fuel’s energy becomes electrical energy and the plant’s efficiency increases. Mathematically, for 1 kWh of output, efficiency is the electrical energy (3,412 BTU) divided by the heat rate (BTU per kWh). So a lower heat rate yields a higher efficiency.

For example, a heat rate of 8,000 BTU/kWh gives about 3,412/8,000 ≈ 42.7% efficiency, while lowering the heat rate to 7,000 BTU/kWh raises efficiency to about 3,412/7,000 ≈ 48.7%.

Why the other statements don’t fit: increasing heat rate does not increase efficiency; it means more fuel is needed per kWh, so efficiency falls. Heat rate is not total energy input per hour; it’s energy input per unit of electricity produced. And heat rate and efficiency are directly connected—one determines the other via the inverse relationship.